The need for equipment and techniques to in-process balance rotating machinery parts is well recognized in industry. A variety of machines and methods are currently available. Typically, they involve a two-step process; first, detecting the amount and location of imbalance in a rotating part or element, and secondly, using this detected information to compensate for the imbalance. Techniques for detecting the amount and location of imbalance are readily available and well understood. However, for many cases including balancing of grinding machinery, only in-process balancing will produce desirable results.
One technique for in-process balancing uses a pair of rotatably movable motor driven eccentric weights which are rotated into position to in-process balance a rotating machine part. Each weight is driven into position by a conventional electric motor through a precision gear train, with the weights being repositioned through the gear train to offset an imbalanced part. Most commonly, this technique is used to balance grinding wheels. However, this technique is only suitable for low speed and low acceleration applications since higher speeds affect the gear train and the corresponding acceleration forces tend to strip the gears. Additionally, it is not suitable for balancing small grinding wheels or small machine parts and it is relatively expensive and can not be mounted on a spindle.
A second existing system utilizes a balance unit having a compartmentalized cylindrical structure which forms four chambers within the inner periphery of the cylinder. A fluid, preferably water, is then injected into each of the chambers from a stationary reservoir through a set of stationary nozzles. The water is introduced into the chambers in a controlled and proportioned manner to compensate for the imbalance. However, this system is very costly and only suitable for balancing large machine elements such as large grinding wheels. Additionally, it is not suitable as a retrofit to balance existing machine parts. Furthermore, fluid leakage can result in water or fluid being splashed onto a factory floor which creates a maintenance problem. Once the chambers are completely filled due to accumulation during the balancing process, the machine part, or grinding wheel, has to be stopped and the chambers have to be emptied in order to start from scratch again. One variation provides for emptying the chambers while the system is in position and in motion, but it increases the overall system cost significantly.
A third balancing system utilizes a self contained four chamber unit similar to the previously cited unit. Each of the chambers is partially filled with Halon, a fluid which evaporates and condenses easily. Pairs of chambers located diagonally opposite another are fluidly interconnected with a tube which allows for the transfer of Halon by heating and evaporating Halon fluid in one of the chambers which forces the evaporated Halon to move to the corresponding chamber diagonally opposite the heated chamber where it is cooled and condensed. However, there are environmental concerns with using Halon. Additionally, response rate is very slow due to the large thermal time constants. Likewise, it is difficult to develop a control strategy for the resulting open loop system, a system which produces large delays that cause overcorrecting, and which makes small corrections tricky to consistently perform. Furthermore, this system is costly and not suitable for machine spindle balancing, or for balancing on small diameter machine parts or driving wheels.
A fourth alternative system is one similar to the preceding third system which has four chambers with diagonally opposed cross chambers connected by a tube routed about the periphery of the unit. This system is self contained. However, a different type of fluid, such as water, is used and a different method is used to transfer fluid in order to balance a part. To facilitate fluid transfer, a pair of peristaltic pumps is controllably operated to transfer the fluid between the chambers. However, while this system is somewhat less expensive than previous systems, it is still too large in size for use with smaller diameter grinding wheels or high speed spindles.